Screen printing originated in China and Japan circa 500 AD using woven silk as the printing mesh to implant the image to be reproduced. The screen printing process is used to apply designs on T-shirts, fabrics for clothing and other textiles as well as for posters, signs, wallpaper, wood, instrument panels nomenclature, watch dials, plastic bottles and cans, and more recently printing conductive circuits for the electronics industry. Screen printing provides a means to uniquely apply a controlled thickness of media to various substrates with many industrial applications. The printing screen is no longer made with "silk" but has been replaced by a variety of fabrics, from course 25 mesh to fine weaves of over 500 threads per inch and many man made fibers such as nylon, polyester, metal clad polyester and even stainless steel wire cloth. The printing screen is usually held in place by a rigid frame commonly of rectangular configuration on which the mesh has been stretched taunt. Newer tubular frames of light weight metal such as aluminum have increasingly become replacements for wooden screens of rectangular cross-section. Screen printing frames of metal with printing screen mesh attached are subject to physical abuse and are often mishandled even during image processing. As a result, the printing screens are subject to tearing or puncturing during such abuse particularly under or near the metal tubular frame area. In use, the screens may become frayed, or torn and the printing frames nicked with burrs that would tear the fine mesh.
Additionally, silk screening is a very messy process, using various media, such as ink, paint or coatings, which flow easily, of a higher viscosity than water and generally of a consistency of a syrup-like molasses. The older style screen printing frames made from wood included vertical walls which easily contained the paint and simplified the screen frame cleanup when the screen printing job was finished. With the new tubular frames the void under the round tubular frame harbors the paint, renders cleanup tedious, if not impossible to remove all traces of ink and very time-consuming. Further, considerable paint finding its way into these areas is not efficiently used, and the screen printing operation ends up with a significant amount of wasted paint or media. To alleviate this problem, the voids were initially covered up with masking tape, having one edge in contact with the tubular metal frame, and the other in contact with the facing surface of the printing screen mesh. Such was found to be unsatisfactory since the tape would come loose and the paint would then flow into the voids and consequently leak out of any open areas of the mesh that are not covered or blocked out near the frame members. Also when removing the tape, it can delaminate and the adhesive remains on the metal frame leaving a sticky residue that is difficult to remove.
Attempts have been made to protect the printing screen and the frame, both from physical abuse and from the flow of printing ink along the periphery into the area of the frames. U.S. Pat. No. 5,327,828 to Earvin V. Barocas et al. issued Jul. 12, 1994 and entitled "CLAMP AND PROCESS FOR PROTECTING PRINTING SCREENS AND FRAMES" provides an extruded plastic screen printing frame protector which seeks to protect the vulnerable areas of the frame and mesh from tearing, while additionally protecting and extending the useful life of the printing screen and frame. In a preferred embodiment of the Barocas et al. patent, a tubular, annular body portion forms a frame engageable clamping member as a resilient impact-resistant bight portion which extends at least about 270.degree. and is shaped complementary to a portion of the contour of the frame member so that the clamp snaps onto and matingly engages the frame member. The relatively thick, highly resilient bight portion is forcibly opened to permit its receiving the frame member internally, whereupon release of the clamping member functions to compressively engage the tubular frame member upon contracting of the open mouth which must be expanded prior to engaging about the frame member. Extending from the arcuate bight portion are a pair of V-shaped leg portions which extend diagonally inward toward each other and which contact each other at the outer free edges of the lips so as to engage and clamp the printing screen. In commercial practice, the Barocas clamp was found to be incapable of pressing on both the frame and the printing screen simultaneously. If effective to clamp onto the frame member, the free edges of the lips could not effectively clamp to opposite sides of the printing screen since there is a lack of pressure being applied to or between the lips, and the lips are separated so they cannot possibly clamp the printing screen. Vice-versa, if the printing screen were clamped resiliently between the edges of the lips, the bight of the clamp would be uncompressed to the exterior of the frame member. Thus, the dual and simultaneous clamping action as described in U.S. Pat. No. 5,327,828 is a physical and mechanical anomaly. In addition, the excessive length of the clamping legs reduces the useable screen area. It is the Applicant's understanding that the Barocas clamp has been commercially discontinued.
It is therefore a primary object of the invention to provide an improved frame protector in the form of a unitary thin wall pliable extruded plastic frame protector body including an integral circular cross-section body portion terminating at one end in an integral, hinged straight arm portion at an angle of about 45.degree. outwardly from a tangent to the first portion at that end and toward a plane defined by the printing screen to facilitate ready pivoting and formation of a vertical wall from the circular cross section first body portion and the printing screen, thereby providing more screening area while still closing voids about the screen printing frame and permitting the use of ordinary masking tape of narrow width to seal the free end of the hinged arm portion to the surface of the printing screen with easy close-off of the printing screen at the periphery and corners of the screen printing frame. The low surface tension of the protector eliminates residue from delamination of the masking tape adhesive.